如何通过iso_c_binding从Fortran调用的C函数接收字符串?

问题描述

我想从Fortran调用C函数并接收在C函数中定义的字符串.我进行了搜索，但到目前为止，找不到有效的，直接的答案.

I want to call a C function from Fortran and receive a string of characters defined in the C function. I searched, but I couldn't find a working, straightforward answer, so far.

实际上，我已经找到一种解决方法:改为接收字符数组，然后使用内在函数 transfer 将结果放入Fortran字符串中.这是我的工作代码.

Actually I have found a workaround: receiving an array of characters instead, then using the intrinsic function transfer to put the result into a Fortran string.Here is my working code.

Fortran主程序:

Fortran main program:

program pr
    implicit none
    character(200) :: stringa

    call strfromc(stringa)
    write (6,*) 'FPR stringa: "', trim(stringa),'"'

    stop
end program pr

Fortran子例程:

Fortran subroutine:

subroutine strfromc(stringa)
    use iso_c_binding
    implicit none

    character(200) :: stringa

    interface
        subroutine getstrfromc(ld,d) bind(c,name='getString')
            import :: c_int, c_ptr
            integer(c_int) :: ld
            type(c_ptr), value :: d
        end subroutine getstrfromc
    end interface

    ! declare a character array of type c_char and sufficient length:
    character(c_char), dimension(200), target :: d1

    integer :: ld1 ! will contain the string length
    integer :: i

    ! the C pointer of character array d1 is passed:
    call getstrfromc(ld1, c_loc(d1))

    ! read the first ld1 elements of array d1 as a character string, which will be returned:
    stringa= transfer(d1(1:ld1), stringa)

    write (6,*) 'SF d1: ', (d1(i),i=1,ld1)
    write (6,*) 'SF stringa: "', trim(stringa),'"'
    write (6,*) ''

    return
end subroutine

C函数:

#include <stdio.h>
#include <string.h>

void getString(int * lw, char * w) {
    printf("Enter a string:\n");
    scanf("%[^\n]", w); //scanning the whole string, including the white spaces

    *lw= strlen(w);

    printf("C: w: %s\n", w);
    printf("C: lw: %d\n", *lw);
    printf("\n");

    return;
}

有人可以提出更直接的方法吗?

Can anyone suggest a more direct way?

推荐答案

为什么不简单地使用 C_CHAR 种?我压缩"了一下您的代码:

Why not simply use C_CHAR kind? I "compressed" your code a bit:

program main
  use, intrinsic :: iso_c_binding, only: C_INT, C_CHAR
  implicit none
  integer         :: lw ! will contain the string length
  character(256)  :: w = "" ! will contain the string; Initialize to empty

  ! C interface
  interface
    subroutine getstrfromc( lw, w ) bind( c, name='getString' )
      import :: C_INT, C_CHAR
      implicit none
      integer(C_INT), intent(out)     :: lw
      character(C_CHAR), intent(out)  :: w(*)
    end subroutine getstrfromc
  end interface

  ! In Fortran variables are passed by default as "pointers".
  call getstrfromc( lw, w )

  ! Write string
  write (*,*) "Fortran: w: ", trim(w)
  write (*,*) "Fortran: lw:", lw

end program main

C函数保持不变.

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